1. Field of the Invention
The present invention relates to the field of medical devices and more particularly to guidewires for use primarily in intra-vascular procedures.
2. Description of the Related Prior Art
A major requirement for medical guidewires and other guiding members, whether they are formed of solid wire or tubular members, is that they have sufficient column strength and stiffness to be pushed through passageways in a patient, such as the patient's vascular system, with minimal kinking or binding. However, the distal section of the guidewire must also be flexible enough to avoid damaging the blood vessel or other body lumen through which it is advanced. Accordingly, efforts have been made to provide guidewires having a favorable combination of both strength and flexibility in order to make them suitable for their intended uses. However, strength for pushing and flexibility for turning without damaging vascular walls tend to be diametrically opposed to one another, such that an increase in one usually involves a decrease in the other, as exemplified below.
The cores of conventional guidewires have been made of many different materials. Two of the more popular materials are stainless steel and Nitinol. In particular, stainless steel has good pushability properties as well as good torque qualities. In turn, guidewire cores formed of such material are generally found suitable for being advanced, and further, for being rotated, so as aid in their being maneuvered, through a patient's vascular system. However, such steel core guidewires tend to be stiff, i.e., not easily bent, and limited in their flexibility. As such, if the steel guidewire is not carefully used, the potential exists for damaging the vessel/body lumen through which it is being advanced. In addition, the steel can be found to bind or kink when rotated since it does not readily flex. As is known, once the guidewire is kinked, it must often be discarded and replaced with a new guidewire.
On the other hand, guidewires formed with Nitinol cores are found to have the flexibility that is warranted for negotiation through a tortuous path in a patient's body lumens or vessels. In turn, when being advanced through a patient's vascular system, such guidewires are found to exhibit lower potential for either damaging the patient's vessel/body lumen or kinking/binding. Unfortunately, such Nitinol guidewires are found to be too soft. As such, they cannot be torqued as readily as stainless steel, thereby limiting their maneuverability. In addition, Nitinol guidewires tend to have good shape memory. Accordingly, they are found to have limited pushability against resistance of tortuosity (e.g., in comparison to guidewires having stainless steel cores) because they tend to straighten out or return to their original shape during their advancement. The shape memory can make it difficult for a physician to shape the tip of the guidewire with his fingers for accessing difficult to reach portions of the patient's vascular system.
As is known, there has been a gradual decrease in the diameter profiles or transverse dimensions of commercially available guidewires, particularly for their use in coronary arteries. Accordingly, these guidewires can be more universally applied in a wide variety of medical procedures. For example, when materials generally known to be rigid or stiff are formed to have decreased profiles, such materials (and the guidewires that they are used in forming) can be found to exhibit greater flexibility. However, associated with the decrease in profile has also been a general loss in pushability.
In light of the above, many conventional guidewires now utilize a wire coil or spring positioned around a distal end section of the guidewire core. In such guidewires, except for the end of the core (which is typically expanded in size), the rest of the distal end section is generally tapered so as to accommodate the coil. In combining the use of such wire coil with a tapered and thinner core for the distal end section, strength as well as flexibility can be achieved in the guidewire. In particular, longitudinal strength along the guidewire distal section is provided via the addition of the wire coil, while lateral flexibility across the guidewire distal section is provided via the tapered core section as well as the inherent lateral flexibility of the wire coil. Unfortunately, there have been a number of limitations found with this design.
In some cases, proximal and distal ends of the wire coil are respectively secured to proximal and distal ends of the distal end section of the core; however, in other cases, none or only one of the wire coil ends are secured to the core. In cases where one or both of the wire coil ends are secured, welding is often used. Welding is advantageous because it involves a relatively easy and inexpensive securing process and effectively provides a rigid point/section of connection for the bodies (i.e., the core and wire coil) being affixed together. Accordingly, when welding is used in securing the wire coil ends to the core, the resulting welds tend to enhance the overall pushability properties of the guidewire at its distal section (via the securement of the wire coil to the core), while still enabling the guidewire's distal section to be flexible (via the tapered core section and the wire coil) so as to be negotiated through a patient's body lumens or vessels. However, because the welds form such a rigid connection, the flexibility of the guidewire, particularly at the welds, is limited. Further, because the welds are rigid, they are generally stressed during repeated bending of the guidewire during its maneuvering. In particular, the welds at the proximal end of the wire coil are generally found to be more stressed than the welds at the distal end of the wire coil because the guidewire often bends at higher degrees along its length than at its end. In turn, such proximally located welds can be found to break after repeated use.
Conversely, in cases where the wire coil ends are not secured to the core, the pushability properties of the guidewire are accordingly found to be limited. In addition, the tapered and thinner (and thereby, softer) core section can be found to not properly engage the wire coil. As such, when rotating the guidewire, there often is not a proper transfer of torque between the core and the wire coil. In turn, the guidewire's maneuverability is also found to be limited. Consequently, the wire coil can be found to kink when being advanced around bends, e.g., in a patient's vascular system.
What are needed are apparatus and systematic methods to address or overcome one or more of the limitations briefly described above with respect to conventional guidewires.